The use of multiple elevator cars in a single elevator hoistway has always posed problems of assignment of cars to calls as well as identifying any particular car that has been assigned to answer a call. In early double-deck elevators, persons desiring to reach an odd floor during up peak traffic would have to enter at an odd floor lobby; similarly for even floors. During down peak, persons entering from an odd or even floor were similarly carried to an odd or even lobby, respectively, near the street level. During off-peak, the dispatching system attempted to answer two calls (either car calls or hall calls) at the same time, if possible, and otherwise simply assigned calls to either the upper or lower deck and delivered any passengers to whichever floors they designated with car calls.
More recently, signage has been provided to indicate to passengers the next stop of an arriving car so that passengers can either enter it or not. This of course does not present adequate service to waiting passengers.
The concept of multiple elevator cars (such as three) within the same hoistway is now known. However, the ability to adequately inform a passenger which arriving car that passenger should enter in order to reach the passenger's destination registered by a call has not been provided adequately.